Ultrasonic sensor, ultrasonic image generating apparatus, and ultrasonic diagnostic apparatus

ABSTRACT

An ultrasonic sensor includes an ultrasonic transducer; a first voltage output circuit to output a transmission voltage signal that oscillates between a first high voltage and a first low voltage, supplied to a first terminal of the ultrasonic transducer; a reception circuit to detect a voltage signal generated at a second terminal of the ultrasonic transducer; and the second voltage output circuit to output a second high voltage smaller than the first high voltage. The first voltage output circuit includes a first switching unit to perform switching between supplying the transmission voltage signal in ultrasonic transmission; and fixing a potential of the first terminal in ultrasonic reception. The second voltage output circuit includes a second switching unit that performs switching between supplying the second high voltage to the second terminal in ultrasonic transmission; and electrically separating the second voltage output circuit from the second terminal in ultrasonic reception.

CROSS-REFERENCE TO RELATED APPLICATION

This patent application is based on and claims priority pursuant to 35U.S.C. § 119(a) to Japanese Patent Application No. 2021-090947, filed onMay 31, 2021, in the Japan Patent Office, the entire disclosure of whichis hereby incorporated by reference herein.

BACKGROUND Technical Field

Embodiments of this disclosure relate to an ultrasonic sensor, anultrasonic image generating apparatus, and an ultrasonic diagnosticapparatus.

Related Art

There is known an ultrasonic sensor that supplies a transmission voltagesignal to a first terminal of an ultrasonic transducer to transmit anultrasonic wave from the ultrasonic transducer to an object, andreceives the ultrasonic wave reflected by the object, so as to detect areception voltage signal generated at a second terminal of theultrasonic transducer.

SUMMARY

An embodiment provides an ultrasonic sensor that includes an ultrasonictransducer, a first voltage output circuit, a reception circuit, and asecond voltage output circuit. The first voltage output circuit isconnected to a first terminal of the ultrasonic transducer. The firstvoltage output circuit outputs a transmission voltage signal thatoscillates between a first high voltage and a first low voltage lowerthan the first high voltage, in accordance with a transmissionfrequency. The transmission voltage signal is supplied to the firstterminal of the ultrasonic transducer to control transmission of anultrasonic wave from the ultrasonic transducer to an object. The firstvoltage output circuit includes a first switching unit that performsswitching between supplying the transmission voltage signal output fromthe first voltage output circuit to the first terminal in ultrasonictransmission, and fixing a potential of the first terminal in ultrasonicreception. The reception circuit is connected to a second terminal ofthe ultrasonic transducer and detects a reception voltage signalgenerated at the second terminal by the ultrasonic wave reflected by theobject. The second voltage output circuit is connected to the secondterminal of the ultrasonic transducer. The second voltage output circuitoutputs a second high voltage having a same polarity as a power supplyvoltage of the reception circuit, the second high voltage having anabsolute value smaller than an absolute value of the first high voltage.The second voltage output circuit includes a second switching unit thatperforms switching between supplying the second high voltage to thesecond terminal in ultrasonic transmission, and electrically separatingthe second voltage output circuit from the second terminal in ultrasonicreception.

In another embodiment, an ultrasonic image generating includes theultrasonic sensor described above; and an image processor configured togenerate an image based on the reception voltage signal received by thereception circuit of the ultrasonic sensor.

In another embodiment, an ultrasonic diagnostic apparatus includes theultrasonic sensor described above; and a display configured to display ashape of the object based on detection by the ultrasonic sensor.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the disclosure and many of the attendantadvantages and features thereof can be readily obtained and understoodfrom the following detailed description with reference to theaccompanying drawings, wherein:

FIG. 1 is a schematic diagram illustrating an example of a configurationof an ultrasonic diagnostic apparatus according to one embodiment;

FIG. 2 illustrates an external configuration of an ultrasonic probe inthe ultrasonic diagnostic apparatus illustrated in FIG. 1 ;

FIG. 3 is a schematic view of one ultrasonic transducer of a transducerunit of the ultrasonic probe illustrated in FIG. 1 ;

FIG. 4 is a schematic diagram illustrating a configuration of anultrasonic diagnostic apparatus according to another embodiment;

FIG. 5 is a block diagram illustrating an example of a configuration ofthe ultrasonic diagnostic apparatus according to one embodiment;

FIG. 6 illustrates an example of an array of ultrasonic transducers ofthe ultrasonic probe according to one embodiment;

FIG. 7 is a circuit diagram illustrating an ultrasonic sensor includingan ultrasonic transducer, a driver that applies a transmission signal,and a reception circuit according to a comparative example;

FIG. 8 is a circuit diagram illustrating an ultrasonic sensor includingan ultrasonic transducer, a driver, and a reception circuit according toanother comparative example;

FIGS. 9A and 9B are circuit diagrams illustrating a circuit operation inultrasonic transmission, performed by the comparative ultrasonic sensorillustrated in FIG. 8 ;

FIGS. 10A and 10B are circuit diagrams illustrating a circuit operationin ultrasonic transmission, performed by the ultrasonic probe serving asan ultrasonic sensor according to one embodiment;

FIGS. 11A and 11B are circuit diagrams illustrating a circuit operationperformed by the ultrasonic sensor illustrated in FIGS. 10A and 10B inultrasonic transmission, when a reception circuit has a power supplyvoltage of 1.2 V;

FIG. 12 is a diagram schematically illustrating a circuit configurationof an ultrasonic sensor according to a modification;

FIG. 13 is a circuit diagram of the ultrasonic sensor illustrated inFIG. 12 ;

FIG. 14 is a diagram illustrating voltages of first and second terminalsof an ultrasonic transducer of the ultrasonic sensor in a case whereswitching of voltage applied to the second terminal is delayed fromswitching of voltage applied to the first terminal, as a comparativeexample;

FIG. 15 is a diagram illustrating switching timings of voltages appliedto the second terminal of the ultrasonic transducer, according to themodification;

FIG. 16 is a diagram illustrating voltages of first and second terminalsof an ultrasonic transducer of the ultrasonic sensor in a case whereswitching of voltage applied to the second terminal is simultaneous withswitching of voltage applied to the first terminal, as a comparativeexample; and

FIG. 17 is a diagram illustrating respective voltage switching ofelements of the driver according to the modification.

The accompanying drawings are intended to depict embodiments of thepresent invention and should not be interpreted to limit the scopethereof. The accompanying drawings are not to be considered as drawn toscale unless explicitly noted. Also, identical or similar referencenumerals designate identical or similar components throughout theseveral views.

DETAILED DESCRIPTION

In describing embodiments illustrated in the drawings, specificterminology is employed for the sake of clarity. However, the disclosureof this specification is not intended to be limited to the specificterminology so selected and it is to be understood that each specificelement includes all technical equivalents that have a similar function,operate in a similar manner, and achieve a similar result.

Referring now to the drawings, embodiments of the present disclosure aredescribed below. As used herein, the singular forms “a,” “an,” and “the”are intended to include the plural forms as well, unless the contextclearly indicates otherwise.

Hereinafter, descriptions are given of an ultrasonic sensor according toan embodiment of the present disclosure. The ultrasonic sensor is usedas an ultrasonic probe of an ultrasonic diagnostic apparatus.

Application of ultrasonic sensors according to embodiments is limited toan ultrasonic probe of an ultrasonic diagnostic apparatus, andapplication to various apparatuses is possible. Further, in the presentembodiment, a human body is the subject of sensing, but the subject isnot limited to a live subject such as a human body. The ultrasonicsensor according to the present embodiment is suitably used in anultrasonic image generating apparatus used in a wide range of fieldssuch as nondestructive inspection, underwater exploration, and personalauthentication, but is also usable in an apparatus other than theultrasonic image generating apparatus.

FIG. 1 is a schematic diagram illustrating an example of a configurationof an ultrasonic diagnostic apparatus according to the presentembodiment.

In FIG. 1 , an ultrasonic diagnostic apparatus 100 includes anultrasonic probe 1. The ultrasonic probe 1 is an ultrasonic sensor thattransmits an ultrasonic wave toward a subject 200 as an object to besensed and receives an ultrasonic wave reflected from the subject 200.The ultrasonic diagnostic apparatus 100 further includes, in anapparatus body 60, a display 61 that visualizes and displays a signal(echo signal) output from the ultrasonic probe 1 and a control panel 62that is operated by an operator.

FIG. 2 illustrates a configuration of the ultrasonic probe 1.

The ultrasonic probe 1 includes a protective layer 2, a transducer unit20, a backing material 3, and a signal processor 10.

The protective layer 2 protects the transducer unit 20. The protectivelayer 2 is preferably made of a material that does not give anunpleasant feeling to the subject 200 when the ultrasonic probe 1 isbrought into contact with the subject 200 and has an acoustic impedancerelatively close to that of a human body. As the protective layer 2, forexample, flexible silicone rubber may be used.

The transducer unit 20 includes an array of ultrasonic transducers 21(see FIG. 3 ) arrayed one dimensionally or two dimensionally. In thepresent embodiment, the ultrasonic transducers 21 are two dimensionallyarrayed, and a three dimensional ultrasonic image is obtained. In thetransducer unit 20, respective signal lines of the ultrasonictransducers 21 are connected to the signal processor 10.

The backing material 3 attenuates unnecessary vibration generated in thetransducer unit 20.

The signal processor 10 performs generation of a transmission signal(transmission voltage signal) for transmitting an ultrasonic wave fromthe transducer unit 20, and processing of a reception signal (receptionvoltage signal) generated by the ultrasonic wave received by thetransducer unit 20. The signal processor 10 is connected to theapparatus body 60 via a cable 40.

FIG. 3 is a schematic view of one ultrasonic transducer 21 of thetransducer unit 20 of the ultrasonic probe 1.

As illustrated in FIG. 3 , the ultrasonic transducer 21 includes asupport plate 23 (a support), a piezoelectric micro-machined ultrasonictransducer (PMUT) chip 22 disposed on the support plate 23, a flexibleboard 24, wiring 25, a connector 27, and an acoustic lens 28. Althoughthe ultrasonic transducer of the present embodiment uses a PMUT,alternatively, another ultrasonic transducer such as a capacitivemicro-machined ultrasonic transducer (CMUT) may be used.

The PMUT chip 22 is connected to the connector 27 via the wiring 25 onthe flexible board 24. The connector 27 is connected to a circuit boardof the signal processor 10. The support plate 23 supports the PMUT chip22 and functions as the backing material 3.

As the acoustic lens 28, for example, an acoustic lens made of siliconeresin is suitably used. The acoustic lens 28 functions as the protectivelayer 2. The acoustic lens 28 focuses the ultrasonic wave transmittedfrom the PMUT chip 22 at a measurement position of the subject 200. Theacoustic lens 28 has a shape (so-called a dome shape) in which a centralarea is thicker than a peripheral area. The acoustic lens 28 contactsthe subject 200 and deforms, thereby tightly contacting the subject 200.Then, acoustic lens 28 artificially refracts ultrasonic waves toconverge by a difference in propagation speed of the ultrasonic waves,caused by a difference in thickness between the central area and theperipheral area.

The acoustic lens 28 and the PMUT chip 22 are bonded to each other by anadhesive 26 as an adhesive layer. The adhesive 26 used for bonding theacoustic lens 28 and the PMUT chip 22 is preferably an adhesive of asilicone-based resin, and preferably has a relatively thin thickness of20 μm or less.

As illustrated in FIG. 4 , an ultrasonic diagnostic apparatus accordingto another embodiment includes a display terminal 50 as a display unitand the ultrasonic probe 1 connected to the display terminal 50 by acable.

FIG. 5 is a block diagram illustrating an example of a configuration ofthe ultrasonic diagnostic apparatus according to the present embodiment.

The apparatus body 60 is connected to the ultrasonic probe 1 via thecable 40. The apparatus body 60 transmits a transmission signal(transmission voltage signal) to the ultrasonic probe 1 via the cable40, thereby causing the ultrasonic probe 1 to transmit ultrasonic waves.Further, the apparatus body 60 receives, from the ultrasonic probe 1, areception signal (reception voltage signal) generated based on thereceived ultrasonic wave by the ultrasonic probe 1, thereby visualizethe internal state of the subject 200 as an ultrasonic image.

The apparatus body 60 of the present embodiment includes the display 61,the control panel 62, a controller 63, a signal converter 64, and animage processor 65 as an image generation unit.

The display 61 includes a monitor such as a liquid crystal display (LCD)and displays an image generated by the image processor 65.

The control panel 62 receives, for example, an instruction operation forinstructing start of diagnosis, an input operation for inputtinginformation related to the subject 200. The control panel 62 includes,for example, an operation panel or a keyboard.

The controller 63 controls operation of the ultrasonic diagnosticapparatus 100. The controller 63 may be implemented by a general-purposecomputer. In particular, the controller 63 is connected to the signalprocessor 10 of the ultrasonic probe 1. The controller 63 transmitstiming information to a timing generator 13 of the signal processor 10via the cable 40. The timing information is for generating operationtimings of a driver 11 and a reception circuit 12 (a delay unit 14 andan adder 15).

The signal converter 64 receives a reception output signal (an outputsignal of the reception circuit 12) from the reception circuit 12 of theultrasonic probe 1 via the cable 40. The signal converter 64 performssignal processing on the received output signal with an amplificationcircuit 66, a band pass filter (BPF) 67, and an analog-to-digital (A/D)converter 68, and outputs the processed signal to the image processor65. To be specific, in the signal converter 64, the amplificationcircuit 66 amplifies the output signal that is weak, and the BPF 67 cutsnoise in a low frequency band and a high frequency band. Then, the A/Dconverter 68 performs A/D conversion for converting the output signal(an analog signal) into a digital signal. Thus, the signal converter 64outputs, as digital data, the reception output signal received from theultrasonic probe 1 to the image processor 65.

All or a part of the signal converter 64 may be included in the signalprocessor 10 of the ultrasonic probe 1.

Under the control of the controller 63, the image processor 65 generatesan image for ultrasonic diagnosis (ultrasonic image) representing theinternal state of the subject 200, using the output signal (digitaldata) received from the signal converter 64. The image processor 65 maybe implemented by processing by a central processing unit (CPU) or aprocessing circuit such as a graphics processing unit (GPU).

The ultrasonic probe 1 is connected to the apparatus body 60 via thecable 40, and includes the transducer unit 20 and the signal processor10. As illustrated in FIG. 5 , the signal processor 10 includes thetiming generator 13, the driver 11, and the reception circuit 12including the delay unit 14 and the adder 15.

The timing generator 13 controls timing of each operation of the driver11 and the reception circuit 12 (the delay unit 14 and the adder 15)based on the timing information from the controller 63 of the apparatusbody 60. Specifically, the timing generator 13 performs timing controlfor the driver 11 to apply transmission signals to the ultrasonictransducers 21 with time differences corresponding to individualdistances thereto, so that ultrasonic waves transmitted from theultrasonic transducers 21 disposed at different positions simultaneouslyarrive at one point of the subject 200. Hereinafter, a suffix indicatingan arrangement number is added to the reference numeral of theultrasonic transducer 21, and the ultrasonic transducer 21 may bereferred to as, for example, a transducer 21-1 or 21-N (N=the number ofthe ultrasonic transducers 21).

In addition, there are differences in arrival times at which theultrasonic waves reflected by the subject 200 reach the ultrasonictransducers 21-1 to 21-N disposed at different positions. Accordingly,for the reception circuit 12, the timing generator 13 performs timingcontrol to correct the arrival time differences. Specifically, when thedistance is short, reflected ultrasonic waves reach the ultrasonictransducer 21 in a short time. Accordingly, the delay unit 14 provides apredetermined delay time to the reception signal of the ultrasonictransducer having a shorter distance. The adder 15 adds the receptionsignals of the ultrasonic transducers 21-1 to 21-N and transmits theaddition result as a reception output signal to the signal converter 64of the apparatus body 60 via the cable 40.

In the present embodiment, for example, as illustrated in FIG. 6 , theultrasonic transducers 21 are arranged in a two dimensional array of 192horizontal lines (channels ch1 to ch192) and 10 vertical lines(sub-arrays sa1 to sa10). In this case, the reception circuit 12receives 1920 reception signals from the ultrasonic transducers 21-1 to21-1920. The reception circuit 12 performs, for each of the channels ch1to ch192, delay addition processing on reception signals from 10ultrasonic transducers 21 on the sub-arrays sa1 to sa10 to be aggregatedinto one piece of information. Thus, the reception circuit 12 transmitsinformation of the channels ch1 to ch192 as 192 pieces of information tothe signal converter 64 via the cable 40. Note that a signalamplification unit may be provided in a preceding stage of the delayunit 14.

Preferably, the distance between the driver 11 and the reception circuit12 and each of the ultrasonic transducers 21-1 to 21-N is as short aspossible. This is for reducing ringing due to wiring between the driver11 and each of the ultrasonic transducers 21-1 to 21-N and voltage dropdue to the wiring, and for inhibiting a decrease in signal-to-noise(S/N) ratio caused by external noise with respect to wiring between thereception circuit 12 to each of the ultrasonic transducers 21-1 to 21-N.Preferably, the signal processor 10 is constructed of one integratedcircuit (IC) and is disposed in the vicinity of the transducer unit 20,to secure high-speed communication of, for example, 10 MHz to 100 MHz incommunication from the timing generator 13 to the driver 11 and thereception circuit 12.

In general, in an ultrasonic sensor such as the ultrasonic probe 1,increasing the frequency of an ultrasonic wave is preferred for thepurpose of increasing the resolution of an ultrasonic image. However,increasing the frequency of the ultrasonic wave results in attenuationof the ultrasonic wave in the object (the subject 200) subjected to theultrasonic wave. Accordingly, it is preferred to transmit a strongerultrasonic wave. Therefore, it is preferred to apply a strongertransmission signal to the ultrasonic transducer 21.

In order to obtain a two dimensional image or a three dimensional imageof an object by an ultrasonic sensor such as the ultrasonic probe 1, adelay circuit (the delay unit 14) corresponding to a distance (arrivaltime) from the ultrasonic transducer 21 to the object, an additioncircuit (the adder 15) for adding reception signals of the plurality ofultrasonic transducers 21, and the like are used. Therefore, when thefrequency of the ultrasonic wave is increased, it is necessary toincrease the speed of the circuit operation of the delay circuit, theaddition circuit, and the like.

For example, assume that the delay circuit (the delay unit 14) is asample-and-hold circuit including a switch and a capacitor, and thereception voltage signal of the 10 MHz is sampled eight times in onecycle. In this example, the operation frequency is as high as 80 Msamples per second. When the sample-and-hold signal of 10 MHz isamplified 10 times by the addition circuit (the adder 15), the bandwidthof the operational amplifier used for signal amplification should beequal to or greater than 1 GHz. Thus, both are high-speed operations. Inorder to realize such a high frequency bandwidth by an integratedcircuit, a fine semiconductor element is used. Since each node of a finesemiconductor element has a low withstand voltage, the power supplyvoltage of the reception circuit 12 (the delay unit 14 and the adder 15)is lowered.

In an ultrasonic sensor such as the ultrasonic probe 1, attenuation ofan ultrasonic wave in a body increases as the frequency of theultrasonic wave increases. Thus, to generate a stronger ultrasonic wave,a high voltage (for example, about 40 V to 200 V) is used for atransmission signal (transmission voltage signal) to be applied to theultrasonic transducers 21 in ultrasonic transmission. Therefore, asemiconductor element having a high withstand voltage is used in acircuit to which a high voltage of a transmission signal is applied. Bycontrast, in ultrasonic reception, the ultrasonic transducer 21 receivesa weak ultrasonic wave (having an intensity of, for example, about 1% ofthe transmitted ultrasonic wave) having been attenuated in an objectsuch as the subject 200. Accordingly, the voltage of the receptionsignal generated by the ultrasonic transducer 21 is small and of ordersof magnitude of μV to mV. Therefore, the reception circuit 12 isappropriately operated by a low power supply voltage such as 3 V or 1.2V. That is, the reception circuit 12 of the ultrasonic sensor can have acircuit configuration of a high frequency bandwidth using a finesemiconductor element.

However, the ultrasonic transducer 21 performs both transmission andreception. Accordingly, in the reception circuit 12 including such afine semiconductor element, application of a high voltage of atransmission signal to the reception circuit 12 in ultrasonictransmission should be avoided.

FIG. 7 is a circuit diagram of a comparative ultrasonic sensor 100Zincluding the ultrasonic transducer 21, the driver 11 (e.g., a drivercircuit) that applies a transmission signal, and the reception circuit12. In the ultrasonic sensor 100Z, a second terminal 21 b of theultrasonic transducer 21 is grounded, and the driver 11 and thereception circuit 12 are connected to a first terminal 21 a of theultrasonic transducer 21 via a switching element SW1.

The ultrasonic sensor 100Z illustrated in FIG. 7 is described in, forexample, Japanese Patent No. 4991722. In the ultrasonic sensor 100Z, inultrasonic transmission, the switching element SW1 is turned off toelectrically separate the reception circuit 12 from the ultrasonictransducers 21, thereby preventing a high voltage of a transmissionsignal of the driver 11 from being applied to the reception circuit 12.In ultrasonic reception, application of the transmission signal from thedriver 11 is turned off, the switching element SW1 is turned on. In thisstate, the reception circuit 12 detects a reception signal generated atthe first terminal 21 a of the ultrasonic transducer 21.

In the ultrasonic sensor 100Z illustrated in FIG. 7 , a semiconductorelement having a high withstand voltage is used in the driver 11 that isconnected to the first terminal 21 a since a high voltage (for example,40 V) is applied to the first terminal 21 a of the ultrasonic transducer21 in ultrasonic transmission. As described above, in the driver 11including a semiconductor element having a high withstand voltage, aparasitic capacitance is relatively large. Therefore, in the ultrasonicsensor 100Z illustrated in FIG. 7 , in ultrasonic reception, electriccharge generated in the ultrasonic transducer 21 flows into theparasitic capacitance in the driver 11, and the reception signaltransmitted to the reception circuit 12 is weakened. As a result,undesirably, the reception sensitivity of the ultrasonic sensor 100Z islowered.

In the ultrasonic sensor 100Z illustrated in FIG. 7 , a weak receptionsignal generated in the ultrasonic transducers 21 in ultrasonicreception is transmitted to the reception circuit 12 via the switchingelement SW1. Therefore, undesirably, the S/N ratio of the receptionsignal transmitted to the reception circuit 12 decreases due to noise inthe switching element SW1.

FIG. 8 is a circuit diagram of another comparative ultrasonic sensor200Z including the ultrasonic transducer 21, the driver 11, and thereception circuit 12. In the ultrasonic sensor 200Z, the driver 11 isconnected to the first terminal 21 a of the ultrasonic transducer 21,and the reception circuit 12 is connected to the second terminal 21 b ofthe ultrasonic transducer 21.

The ultrasonic sensor 200Z illustrated in FIG. 8 is described in, forexample, Japanese Patent No. 6616296. In the ultrasonic sensor 200Z, thesecond terminal 21 b of the ultrasonic transducer 21 is grounded via aswitching element SW2.

In the ultrasonic sensor 200Z illustrated in FIG. 8 , in ultrasonictransmission, the switching element SW2 is turned on to keep the secondterminal 21 b of the ultrasonic transducer 21 at 0 V, so as to preventapplication of a high voltage of the transmission signal of the driver11 to the reception circuit 12. In ultrasonic reception, application ofthe transmission signal from the driver 11 is stopped, and a switchingelement SW3 is turned on, to keep the potential of the first terminal 21a of the ultrasonic transducer 21 at 0 V. Further, the switching elementSW2 is turned off, to electrically separate the second terminal 21 b ofthe ultrasonic transducer 21 from the ground. Then, the receptioncircuit 12 detects the reception signal generated at the second terminal21 b of the ultrasonic transducer 21.

In the ultrasonic sensor 200Z illustrated in FIG. 8 , the receptioncircuit 12 is connected to the second terminal 21 b of the ultrasonictransducer 21 different from the first terminal 21 a to which the driver11 is connected. This configuration suppresses weakening of thereception signal transmitted to the reception circuit 12 due to theparasitic capacitance of the driver 11 including a semiconductor elementhaving a high withstand voltage. Accordingly, degradation of thereception sensitivity of the ultrasonic sensor 200Z is suppressed.

The ultrasonic sensor 200Z illustrated in FIG. 8 does not includes aswitching element between the second terminal 21 b of the ultrasonictransducer 21 and the reception circuit 12. Therefore, a weak receptionsignal generated in the ultrasonic transducer 21 in ultrasonic receptionis transmitted to the reception circuit 12 without passing through theswitching element. This configuration also eliminates a decrease in theS/N ratio of the reception signal caused by the switching element.

However, in the ultrasonic sensor 200Z illustrated in FIG. 8 , thesecond terminal 21 b of the ultrasonic transducer 21 is grounded via theswitching element SW2. When the switching element SW2 is a semiconductorelement, there is a risk that a voltage out of the allowable voltagerange is applied to the reception circuit 12 in ultrasonic transmission.

FIGS. 9A and 9B are circuit diagrams illustrating a circuit operation inultrasonic transmission, performed by the comparative ultrasonic sensor200Z illustrated in FIG. 8 .

In the comparative ultrasonic sensor 200Z illustrated in FIGS. 9A and9B, the switching element SW2 connected between the second terminal 21 bof the ultrasonic transducer 21 and the ground is an n-type metal-oxidesemiconductor field-effect transistor (MOSFET). The driver 11 includescomplementary metal-oxide-semiconductor field effect transistors(CMOSFETs), specifically, a switching element SWA that is a p-typeMOSFET (third MOS transistor) and a switching element SWB that is ann-type MOSFET (fourth MOS transistor). A drain terminal of the switchingelement SWA (p-type MOSFET) and a drain terminal of the switchingelement SWB (n-type MOSFET) are connected to the first terminal 21 a ofthe ultrasonic transducer 21. A source terminal of the switching elementSWA is supplied with voltage Vdd (for example, 40 V). A source terminalof the switching element SWB is supplied with voltage Vss (for example,0 V). The driver 11 outputs a transmission signal (transmission voltagesignal) by repeatedly turning on and off the switching element SWA(p-type MOSFET) and turning on and off the switching element SWB (n-typeMOSFET) according to a predetermined transmission frequency. Forexample, the predetermined frequency is set experimentally by amanufacturer of the ultrasonic sensor in advance.

As illustrated in FIGS. 9A and 9B, the ultrasonic transducer 21 can beunderstood as a capacitance model, to be exact, aninductance-capacitance-resistance (LCR) model. In ultrasonictransmission, the switching element SW2 that is an n-type MOSFET is kepton, and the second terminal 21 b of the ultrasonic transducer 21 isgrounded. Therefore, as illustrated in FIG. 9A, as the switchingelements SWA and SWB are turned on and off, a current instantaneouslyflows through the ultrasonic transducer 21.

At a time when the switching element SWA (p-type MOSFET) is switchedfrom off to on and the switching element SWB (n-type MOSFET) is switchedfrom on to off (at charging), the voltage applied to the first terminal21 a of the ultrasonic transducer 21 is switched from a first lowvoltage of 0 V to a first high voltage of 40 V. At this time (atcharging), as illustrated in FIG. 9A, an instantaneous current flowsthrough the ultrasonic transducers 21 from the first terminal 21 atoward the second terminal 21 b. This current flows through theswitching element SW2 that is an n-type MOSFET toward the ground side.Although the voltage of the second terminal 21 b of the ultrasonictransducer 21 is slightly raised by the current flowing through theswitching element SW2 that is an n-type MOSFET, the voltage is within arange of 0+α V (α<1 V). The voltage of 0+α V is applied to the receptioncircuit 12 connected to the second terminal 21 b of the ultrasonictransducer 21. Since the voltage of 0+α V has the same polarity as thepower supply voltage (3 V) of the reception circuit 12 and is equal toor lower than the power supply voltage, the voltage is within theallowable voltage range of the reception circuit 12 and does not damageor destroy the reception circuit 12.

On the other hand, when the switching element SWA that is a p-typeMOSFET is switched from on to off and the switching element SWB that isan n-type MOSFET is switched from off to on (at discharge), the voltageapplied to the first terminal 21 a of the ultrasonic transducer 21 isswitched from the first high voltage of 40 V to the first low voltage of0 V. At this time (at discharge), as illustrated in FIG. 9B, aninstantaneous current flows through the ultrasonic transducer 21 fromthe second terminal 21 b toward the first terminal 21 a. This currentflows through the switching element SW2 that is an n-type MOSFET fromthe ground side. The voltage at the second terminal 21 b of theultrasonic transducer 21 is lowered by the current flowing through theswitching element SW2 (n-type MOSFET). Accordingly, the voltage at thesecond terminal 21 b is lowered from 0 V to about 0-0.7 V at which thebody diode of the switching element SW2 is turned on. Since the voltageof 0-0.7 V (=−0.7 V) has a polarity opposite to that of the power supplyvoltage (3 V) of the reception circuit 12, the voltage is out of theallowable voltage range of the reception circuit 12 and may damage ordestroy the reception circuit 12.

By contrast, referring to FIGS. 10A and 10B, a description is given of acircuit operation at transmission in the ultrasonic sensor serving asthe ultrasonic probe 1 according to the present embodiment.

The ultrasonic probe 1 (ultrasonic sensor) according to the presentembodiment includes a second voltage output unit 19 connected to thesecond terminal 21 b of the ultrasonic transducer 21 via a switchingelement SW4 (second switching unit) that is a p-type MOSFET. The secondvoltage output unit 19 outputs a second high voltage (e.g., 3 V) havingthe same polarity as the power supply voltage (e.g., 3 V) of thereception circuit 12 and having an absolute value smaller than the firsthigh voltage (e.g., 40 V) applied to the first terminal 21 a of theultrasonic transducer 21. The structures of the driver 11 and thereception circuit 12 are the same as those illustrated in FIGS. 9A and9B.

In the ultrasonic probe 1 (ultrasonic sensor) of the present embodiment,in ultrasonic transmission, the switching element SW4 is kept on, andthe second high voltage (3 V) output from the second voltage output unit19 is supplied to the second terminal 21 b of the ultrasonic transducers21. Although the power supply voltage of the second voltage output unit19 of the present embodiment is equal to that of the reception circuit12, that is, outputs 3 V that is equal to the power supply voltage ofthe reception circuit 12, the configuration is not limited thereto.Alternatively, the second voltage output unit 19 may output a voltagedifferent from the power supply voltage of the reception circuit 12. Forexample, the second voltage output unit 19 may output any high voltagehaving the same polarity as the power supply voltage of the receptioncircuit 12 and not exceeding the absolute value of the power supplyvoltage of the reception circuit 12.

At a time when the switching element SWA that is a p-type MOSFET isswitched from on to off and the switching element SWB that is an n-typeMOSFET is switched from off to on (at discharge), the voltage applied tothe first terminal 21 a of the ultrasonic transducer 21 is switched fromthe first high voltage of 40 V to the first low voltage of 0 V. At thistime (at discharge), as illustrated in FIG. 10B, an instantaneouscurrent flows through the ultrasonic transducer 21 from the secondterminal 21 b toward the first terminal 21 a. This current flows throughthe switching element SW4 that is an p-type MOSFET. The current flowingthrough the switching element SW4 that is a p-type MOSFET slightlylowers the voltage of the second terminal 21 b of the ultrasonictransducer 21 from 3 V, but the voltage of the second terminal 21 b doesnot become lower than 0 V. This voltage is equal to or lower than thepower supply voltage (3 V) of the reception circuit 12 and within theallowable voltage range of the reception circuit 12. Therefore, thereception circuit 12 is not damaged or broken.

At a time when the switching element SWA (p-type MOSFET) is switchedfrom off to on and the switching element SWB (n-type MOSFET) is switchedfrom on to off (at charging), the voltage applied to the first terminal21 a of the ultrasonic transducer 21 is switched from the first lowvoltage of 0 V to the first high voltage of 40 V. At this time (atcharging), as illustrated in FIG. 10A, an instantaneous current flowsthrough the ultrasonic transducers 21 from the first terminal 21 atoward the second terminal 21 b. This current flows through theswitching element SW4 that is a p-type MOSFET. The current flowingthrough the switching element SW4 that is a p-type MOSFET raises thevoltage at the second terminal 21 b of the ultrasonic transducer 21 toabout 3+0.7 V at which the body diode of the switching element SW2 isturned on. The voltage of 3+0.7 V (=3.7 V) is greater than the powersupply voltage (3 V) of the reception circuit 12, but is within theallowable voltage range of the reception circuit 12. Normally, theallowable voltage range of the reception circuit 12 is equal to orsmaller than 1.4 times (4.2 V) the power supply voltage (3 V).Therefore, the reception circuit 12 is not damaged or broken.

Next, a modification of the circuit configuration of the ultrasonicsensor (ultrasonic probe 1) according to the present embodiment will bedescribed.

For speeding up the circuit operation of the reception circuit 12 inorder to cope with increases in the frequency of the ultrasonic wave, afine semiconductor element is used in the reception circuit 12, and thepower supply voltage is lowered accordingly. In the presentmodification, the power supply voltage of the reception circuit 12 isset to 1.2 V, which is lower than 3 V in the above-described embodiment.

FIGS. 11A and 11B are circuit diagrams illustrating a circuit operationin ultrasonic transmission in a case where the power supply voltage ofthe reception circuit 12 is set to 1.2 V in the ultrasonic probe 1(ultrasonic sensor) illustrated in FIGS. 10A and 10B.

FIG. 12 is a diagram schematically illustrating a circuit configurationof the ultrasonic probe 1 (ultrasonic sensor) according to the presentmodification. In the present modification, the driver 11 includes firstand second drive circuits 11A and 11B.

In the case where the power supply voltage of the reception circuit 12is lowered to 1.2 V, as illustrated in FIG. 11B, when an instantaneouscurrent flows from the second terminal 21 b to the first terminal 21 ain the ultrasonic transducers 21 (at the time of discharge), the voltageat the second terminal 21 b of the ultrasonic transducers 21 is slightlylowered from 1.2 V. Therefore, the reception circuit 12 is not damagedor broken.

However, as illustrated in FIG. 11A, when an instantaneous current flowsthrough the ultrasonic transducers 21 from the first terminal 21 atoward the second terminal 21 b (at charging), the voltage at the secondterminal 21 b of the ultrasonic transducers 21 reaches the vicinity of1.2+0.7 V at which the body diode of the switching element SW2 is turnedon. The voltage of 1.2+0.7 V (=1.9 V) is greater than the allowablevoltage range (1.68 V) of the reception circuit 12 which is 1.4 timesthe power supply voltage (1.2 V) of the reception circuit 12. There is arisk that the reception circuit 12 is damaged or broken.

FIG. 13 is a circuit diagram illustrating a detail of the ultrasonicprobe 1 (ultrasonic sensor) according to the present modification.

In the driver 11 according to the present modification, the first drivecircuit 11A includes the first voltage output unit to output thetransmission signal to the first terminal 21 a of the ultrasonictransducer 21 and the first switching unit. In the first drive circuit11A, similar to those illustrated in FIGS. 9A to 11B, the switchingelement SWA (p-type MOSFET, third MOS transistor) has the sourceterminal to which a first high voltage (40V) is applied from a powersupply Vdd1, the switching element SWB (n-type MOSFET, fourth MOStransistor) has the source terminal to which a first low voltage (0V) isapplied from a power supply Vss1, and the drain terminal of theswitching element SWA (p-type MOSFET) and the drain terminal of theswitching element SWB (n-type MOSFET) are connected to the firstterminal 21 a of the ultrasonic transducer 21. Hereinafter the firsthigh voltage applied from the power supply Vdd1 is referred to as“voltage Vdd1,” and the first low voltage applied from the power supplyVss1 is referred to as “voltage Vss1.”

By contrast, in the driver 11 of the present modification, the secondvoltage output unit and the second switching unit (second drive circuit11B) for supplying voltage to the second terminal 21 b of the ultrasonictransducers 21 have a configuration different from those illustrated inFIGS. 9A to 11B. Specifically, in the second drive circuit 11B, aswitching element SWC (p-type MOSFET, first MOS transistor) has a sourceterminal to which a second high voltage (1.2 V) is applied from a powersupply Vdd2, a switching element SWD (n-type MOSFET, second MOStransistor) has a source terminal to which a second low voltage, (groundvoltage=0 V) is applied from a power supply Vss2, and a drain terminalof the switching element SWC (p-type MOSFET) and a drain terminal of theswitching element SWD (n-type MOSFET) are connected to the secondterminal 21 b of the ultrasonic transducers 21. Hereinafter the secondhigh voltage applied from the power supply Vdd2 is referred to as“voltage Vdd2,” and the second low voltage applied from the power supplyVss2 is referred to as “voltage Vss2.”

In the present modification, switching operation between transmissionand reception of ultrasonic waves is performed according to an operationswitching signal rc.

Specifically, an ultrasonic wave is transmitted when the operationswitching signal rc is at the low (L) level, and the ultrasonic wave isreceived when the operation switching signal rc is at the high (H)level.

Specifically, for transmission of ultrasonic waves, a transmission pulsesignal IN corresponding to a predetermined transmission frequencytransmitted from the timing generator 13 is input to the driver 11.Since the operation switching signal rc is at the H level, thetransmission pulse signal IN input to the driver 11 is input to thesecond drive circuit 11B as is (second transmission pulse signal IN).The second transmission pulse signal IN input to the second drivecircuit 11B is input to a gate terminal pg2 of the switching element SWC(p-type MOSFET) and a gate terminal ng2 of the switching element SWD(n-type MOSFET) via delay circuits 18C and 18D.

On the other hand, the driver 11 further includes an inverter 16 (NOTcircuit) that inverts the transmission pulse signal to a firsttransmission pulse signal INb (inverted signal) to be input to the firstdrive circuit 11A.

The first transmission pulse signal INb input to the first drive circuit11A is then input to a gate terminal pg1 of the switching element SWA(p-type MOSFET) and a gate terminal ng1 of the switching element SWB(n-type MOSFET) via first and second level shift circuits 17 a and 17 band delay circuits 18A and 18B.

For example, the first and second level shift circuits 17 a and 17 bfunction as follows. When the transmission pulse signal IN is a voltagesignal that repeatedly oscillates between 1.2 V and 0 V, the first levelshift circuit 17 a outputs a voltage signal that repeatedly oscillatesbetween 5 V and 0 V, and the second level shift circuit 17 b outputs avoltage signal that repeatedly oscillates between 40 V and 35 V.

Each of the delay circuits 18A to 18D delays the changing timing onlyone of when the input signal changes from the H level to the L level andwhen the input signal changes from the L level to the H level. Forexample, the delay circuit 18A delays the changing timing by 10 ns whenthe input signal changes from the H level to the L level. The delaycircuit 18B delays the changing timing by 10 ns when the input signalchanges from the L level to the H level. The delay circuit 18C delaysthe changing timing by 5 ns when the input signal changes from the Hlevel to the L level. The delay circuit 18D delays the changing timingby 5 ns when the input signal changes from the L level to the H level.

In the present modification, in ultrasonic transmission, the firsttransmission pulse signal INb at the L level is input to the first drivecircuit 11A when the transmission pulse signal IN is at the H level.Then, the gate terminals pg1 and ng1 of the switching elements SWA andSWB become the L level. At this time, since the switching element SWAthat is a p-type MOSFET is turned on and the switching element SWB thatis an n-type MOSFET is turned off, the voltage Vdd1 (40 V) is applied asa voltage V1 (FIG. 13 ) to the first terminal 21 a of the ultrasonictransducer 21.

When the transmission pulse signal IN is at the L level, the firsttransmission pulse signal INb at the H level is input to the first drivecircuit 11A, and the gate terminals pg1 and ng1 of the switchingelements SWA and SWB become the H level. At this time, since theswitching element SWA that is a p-type MOSFET is turned off and theswitching element SWB that is an n-type MOSFET is turned on, the voltageVss1 (0 V) is applied as the voltage V1 (FIG. 13 ) to the first terminal21 a of the ultrasonic transducer 21.

Therefore, the first terminal 21 a of the ultrasonic transducer 21 issupplied with a transmission voltage signal that oscillates between 40 Vand 0 V, in response to switching between the H level and the L level ofthe transmission pulse signal IN corresponding to the predeterminedtransmission frequency.

By contrast, in ultrasonic transmission, when the transmission pulsesignal IN is at the H level, the second transmission pulse signal IN atthe H level is input to the second drive circuit 11B. Then, the gateterminals pg2 and ng2 of the switching elements SWC and SWD are at the Hlevel. At this time, since the switching element SWC that is a p-typeMOSFET is turned off and the switching element SWD that is an n-typeMOSFET is turned on, the voltage Vss2 (0 V) is applied as a voltage V2(FIG. 13 ) to the second terminal 21 b of the ultrasonic transducer 21.

On the other hand, when the transmission pulse signal IN is at the Llevel, the second transmission pulse signal IN at the L level is inputto the second drive circuit 11B. Then, the gate terminals pg2 and ng2 ofthe switching elements SWC and SWD become the L level. At this time,since the switching element SWC that is a p-type MOSFET is turned on andthe switching element SWD that is an n-type MOSFET is turned off, thevoltage Vdd2 (1.2 V) is applied as the voltage V2 (FIG. 13 ) to thesecond terminal 21 b of the ultrasonic transducer 21.

Therefore, the second terminal 21 b of the ultrasonic transducer 21 issupplied with a transmission voltage signal oscillating between 0 V and1.2 V, in response to switching between the H level and the L level ofthe transmission pulse signal IN corresponding to the predeterminedtransmission frequency.

As described above, in the present modification, in ultrasonictransmission, repeatedly, supply of the voltage Vdd2 (1.2 V) to thesecond terminal 21 b is turned off during a period in which the firsthigh voltage (40 V) is applied from the power supply Vdd1 to the firstterminal 21 a, and is turned on during a period in which the voltageVss1 (0 V) is applied to the first terminal 21 a. With this operation,with respect to the transmission voltage signal (voltage signal thatoscillates between 40 V and 0 V) applied to the first terminal 21 a ofthe ultrasonic transducer 21, a voltage signal (voltage signal thatoscillates between 0 V and 1.2 V), which is an inverted signal, isapplied to the second terminal 21 b of the ultrasonic transducer 21.

In this case, when the voltage applied to the first terminal 21 a of theultrasonic transducer 21 is switched from the first high voltage of 40 Vto the first low voltage of 0 V, the voltage applied to the secondterminal 21 b of the ultrasonic transducer 21 is switched from thesecond low voltage of 0 V (supply of the second high voltage of 1.2 V isoff) to the second high voltage of 1.2 V. At this timing (switching from40 V to 0 V), as illustrated in FIG. 13 , a current I2 instantaneouslyflows through the ultrasonic transducers 21. As the current I2 flowsthrough the body diode of the switching element SWD (n-type MOSFET) ofthe second drive circuit 11B, the potential of the second terminal 21 bof the ultrasonic transducer 21 is lowered by about 0.7 V.

At this time, in the present modification, the voltage applied to thesecond terminals 21 b of the ultrasonic transducers 21 is switched fromthe second low voltage of 0 V to the second high voltage of 1.2 V. As aresult, the potential of the second terminal 21 b of the ultrasonictransducer 21 rises from 0 V. With this configuration, even when thepotential of the second terminal 21 b of the ultrasonic transducer 21 islowered by the current I2, the second terminal 21 b of the ultrasonictransducer 21 is prevented from having a negative potential. Then, thereception circuit 12 is prevented from being applied with a negativevoltage outside the allowable voltage range (a voltage having a polarityopposite to that of the power supply voltage of the reception circuit12.

Further, in the present modification, when the voltage applied to thefirst terminal 21 a of the ultrasonic transducer 21 is switched from thefirst low voltage of 0 V to first high voltage of 40 V, the voltageapplied to the second terminal 21 b of the ultrasonic transducer 21 isswitched from the second high voltage of 1.2 V (supply of the secondhigh voltage is on) to the second low voltage of 0 V (supply of thesecond high voltage is off). At this timing (switching from 0 V to 40V), as illustrated in FIG. 13 , a current I1 instantaneously flowsthrough the ultrasonic transducers 21. As the current I1 flows throughthe body diode of the switching element SWC (p-type MOSFET) of thesecond drive circuit 11B, the potential of the second terminal 21 b ofthe ultrasonic transducers 21 is raised by about 0.7 V.

At this time, in the present modification, the voltage applied to thesecond terminal 21 b of the ultrasonic transducer 21 is switched fromthe second high voltage of 1.2 V to the second low voltage of 0 V.Accordingly, the potential of the second terminal 21 b of the ultrasonictransducer 21 lowers from the second high voltage of 1.2 V. As a result,even when the potential of the second terminal 21 b of the ultrasonictransducers 21 is raised by the current I1, the potential of the secondterminal 21 b of the ultrasonic transducer 21 is prevented from risingsignificantly (approximately 0.7 V) from 1.2 V, and is keptapproximately at the second high voltage of 1.2 V or lower.

Therefore, according to the present modification, even in the receptioncircuit 12 having a low power supply voltage (1.2 V) and including afine semiconductor element, application of an overvoltage exceeding theallowable voltage range to the reception circuit 12 is prevented,thereby preventing damage or destruction of the reception circuit 12.

In ultrasonic transmission, there is a risk of application of a voltageoutside the allowable voltage range to the reception circuit 12 when theswitching of the voltage applied to the second terminal 21 b of theultrasonic transducers 21 is delayed from the switching of the voltageapplied to the first terminal 21 a of the ultrasonic transducers 21.

FIG. 14 is a diagram illustrating the voltages of the first terminal 21a and the second terminal 21 b of the ultrasonic transducers 21 when theswitching of the voltage applied to the second terminal 21 b of theultrasonic transducers 21 is delayed from the switching of the voltageapplied to the first terminal 21 a of the ultrasonic transducers 21.

In ultrasonic transmission, the current I1 instantaneously flows throughthe ultrasonic transducer 21 immediately after the switching of thevoltage applied to the first terminal 21 a of the ultrasonic transducer21 from the first low voltage of 0 V to the first high voltage of 40 V,that is, switching of the logical output value of the first terminal 21a in FIG. 14 from the L level to the H level. Then, the potential of thesecond terminal 21 b of the ultrasonic transducer 21 is raised by about0.7 V as illustrated in FIG. 14 . At this time, since the switching ofthe voltage applied to the second terminal 21 b of the ultrasonictransducer 21 is delayed (the logical output value of the secondterminal 21 b is still at the H level as illustrated in FIG. 14 ), thesecond high voltage of 1.2 V is applied to the second terminal 21 b ofthe ultrasonic transducer 21. Therefore, the potential of the secondterminal 21 b of the ultrasonic transducer 21 is raised from 1.2 V byabout 0.7 V, and a voltage of 1.2+0.7 V (1.9 V) is applied to thereception circuit 12. This voltage is greater than the allowable voltagerange (1.68 V) of the reception circuit 12 which is 1.4 times the powersupply voltage (1.2 V) of the reception circuit 12. There is a risk thatthe reception circuit 12 is damaged or broken.

Similarly, the current I2 instantaneously flows through the ultrasonictransducer 21 immediately after the switching of the voltage applied tothe first terminal 21 a of the ultrasonic transducer 21 from the firsthigh voltage of 40 V to the first low voltage of 0 V, that is, switchingof the logical output value of the first terminal 21 a in FIG. 14 fromthe H level to the L level. Then, the potential of the second terminal21 b of the ultrasonic transducer 21 is lowered by about 0.7 V. At thistime, since the switching of the voltage applied to the second terminal21 b of the ultrasonic transducer 21 is delayed (the logical outputvalue of the second terminal 21 b is still at the L level as illustratedin FIG. 14 ), the second low voltage of 0 V is applied to the secondterminal 21 b of the ultrasonic transducer 21. Therefore, the potentialof the second terminal 21 b of the ultrasonic transducer 21 is loweredfrom 0 V by about 0.7 V, and a voltage of 0−0.7 V (−0.7 V) is applied tothe reception circuit 12. There is a risk that voltage having thepolarity opposite to that of the power supply voltage (1.2 V) of thereception circuit 12 (voltage outside the allowable voltage range) isapplied to the reception circuit 12, which may damage or destroy thereception circuit 12.

FIG. 15 is a diagram illustrating switching times of voltages applied tothe second terminal 21 b of the ultrasonic transducer 21 in the presentmodification.

In the ultrasonic transducer 21 according to the present modification,the voltage applied to the second terminal 21 b is switched before thevoltage applied to the first terminal 21 a of the ultrasonic transducer21 is switched.

In the present modification, in ultrasonic transmission, the voltageapplied to the first terminal 21 a of the ultrasonic transducer 21 isswitched from the first low voltage of 0 V to the first high voltage of40 V, that is, switching of the logical output value of the firstterminal 21 a of FIG. 15 from the L level to the H level, after thevoltage applied to the second terminal 21 b of the ultrasonic transducer21 is switched from the second high voltage of 1.2 V to the second lowvoltage of 0 V (after the switching of the logical output value of thesecond terminal 21 b from the H level to the L level as illustrated inFIG. 15 ). Therefore, the voltage of the second terminal 21 b of theultrasonic transducer 21 has already dropped from 1.2 V toward 0 V. Evenif the current I1 flows through the ultrasonic transducer 21, thepotential of the second terminal 21 b of the ultrasonic transducer 21does not exceed 1.2 V as illustrated in FIG. 15 . Therefore, a voltageexceeding the allowable voltage range is not applied to the receptioncircuit 12, and damage or breakage of the reception circuit 12 isprevented.

Similarly, in the present modification, in ultrasonic transmission, thevoltage applied to the first terminal 21 a of the ultrasonic transducer21 is switched from the first high voltage of 40 V to the first lowvoltage of 0 V, that is, the logical output value of the first terminal21 a in FIG. 15 is switched from the H level to the L level, after thevoltage applied to the second terminal 21 b of the ultrasonic transducer21 is switched from the second low voltage of 0 V to the second highvoltage of 1.2 V (after the logical output value of the second terminal21 b is switched from the L level to the H level as illustrated in FIG.15 ). Therefore, the voltage of the second terminal 21 b of theultrasonic transducer 21 has already rose from 0 V toward 1.2 V. Even ifthe current I2 flows through the ultrasonic transducer 21, the potentialof the second terminal 21 b of the ultrasonic transducer 21 does notdrop below 0 V as illustrated in FIG. 15 . Therefore, a voltage outsidethe allowable voltage range is not applied to the reception circuit 12,and the reception circuit 12 is prevented from being damaged or broken.

In the present modification, with such a transmission operation, thefirst terminal 21 a of the ultrasonic transducer 21 is supplied with atransmission voltage signal that oscillates between approximately −0.7 V(=Vss1 (0 V)−0.7 V) and 40.7 V (=Vdd1 (40 V)+0.7 V).

For example, as illustrated in FIG. 15 , during a period from when thesecond terminal 21 b switches from the L level to the H level to whenthe first terminal 21 a switches from the H level to the L level, theoutput voltage of the second voltage output unit changes first.Therefore, the body diode of the switching element SWC (p-type MOSFET)is likely to turn on, and it is possible that a voltage of about 40.7 Vis applied to both the switching element SWA and the switching elementSWB of the first drive circuit 11A (the first voltage output unit).However, the voltage of 40.7 V is within the allowable voltage range ofthe switching elements SWA and SWB. The allowable voltage range isnormally equal to or lower than 1.4 times the power supply voltage (40V×1.4=56 V). The switching elements SWA and SWB having such a highwithstand voltage are not damaged.

During a period from when the second terminal 21 b is switched from theH level to the L level until when the first terminal 21 a is switchedfrom the L level to the H level, the output voltage of the secondvoltage output unit changes first, and thus the body diode of the n-typeMOSFET is likely to be turned on. In this case, it is possible that avoltage of about −0.7 V is applied to the switching element SWA and theswitching element SWB of the first voltage output unit, but theswitching elements SWA and SWB having a high withstand voltage are notdamaged.

The voltage applied to the second terminal 21 b of the ultrasonictransducer 21 may be switched at the same time as the switching of thevoltage applied to the first terminal 21 a of the ultrasonic transducers21. As illustrated in FIG. 16 , such a configuration also preventsapplication of a voltage out of the allowable voltage range to thereception circuit 12 and prevents damage or destruction of the receptioncircuit 12.

However, even when such simultaneous switching is designed, due to somefactors, the switching of the voltage applied to the second terminal 21b of the ultrasonic transducer 21 may be delayed from the switching ofthe voltage applied to the first terminal 21 a of the ultrasonictransducers 21.

In such a situation, a voltage outside the allowable voltage range isapplied to the reception circuit 12, and the reception circuit 12 may bedamaged or broken.

By contrast, in the present modification in which the switching of thevoltage applied to the second terminal 21 b of the ultrasonic transducer21 is set prior to the switching of the voltage applied to the firstterminal 21 a of the ultrasonic transducers 21, delay of the switchingof the voltage applied to the second terminal 21 b of the ultrasonictransducer 21 from the switching of the voltage applied to the firstterminals 21 a of the ultrasonic transducers 21 is prevented. Therefore,this configuration stably prevents a voltage outside the allowablevoltage range from being applied to the reception circuit 12, and moresafely prevents damage or destruction of the reception circuit 12.

FIG. 17 is a diagram illustrating voltage switching of the elements ofthe driver 11 in the present modification.

FIG. 17 illustrates the relationship among the first transmission pulsesignal INb, the second transmission pulse signal IN, the gate terminalpg1 of the switching element SWA and the gate terminal ng1 of theswitching element SWB in the first drive circuit 11A, the gate terminalpg2 of the switching element SWC and the gate terminal ng2 of theswitching element SWD in the second drive circuit 11B, and the voltageof the first terminal 21 a and the voltage of the second terminal 21 bof the ultrasonic transducers 21. In FIG. 17 , for ease ofunderstanding, it is assumed that the delay time of the inverter 16 andthe level shift circuits 17 a and 17 b is 0.

In the first drive circuit 11A, the delay circuits 18A and 18B provide adelay of 10 ns, and there is a period of 10 ns during which the twoswitching elements SWA and SWB are off.

Similarly, in the second drive circuit 11B, the delay circuits 18C and18D provide a delay of 5 ns, and there is a period of 5 ns in which thetwo switching elements SWC and SWD are off. Owing to the delay timedifference, in the present modification, the voltage of the secondterminal 21 b applied from the second drive circuit 11B starts changingin potential for inverting the output logic value earlier by 5 ns thanthe voltage of the first terminal 21 a applied from the first drivecircuit 11A.

In the present modification, in ultrasonic reception, one of theswitching elements SWA and SWB of the first drive circuit 11A is kepton, and the potential of the first terminal 21 a of the ultrasonictransducer 21 is fixed at Vdd1 (=40 V) or Vss1 (=0 V). In the example ofFIG. 13 , since the operation switching signal rc is at the H level, thepotential of the first terminal 21 a of the ultrasonic transducer 21 isfixed to Vss1 (=0 V) regardless of the transmission pulse signal IN. Onthe other hand, since the operation switching signal rc is at the Hlevel, both of the switching elements SWA and SWB of the second drivecircuit 11B are kept off regardless of the transmission pulse signal IN.In practice, the second terminal 21 b of the ultrasonic transducer 21 iskept at a predetermined potential via a high resistance, and thereception circuit 12 detects a reception signal generated at the secondterminal 21 b of the ultrasonic transducer 21.

The configurations described above are examples, and various aspects ofthe present disclosure provide, for example, the following effects,respectively.

Aspect 1

Aspect 1 concerns an ultrasonic sensor (e.g., the ultrasonic probe 1)that applies a transmission voltage signal to a first terminal (thefirst terminal 21 a) of an ultrasonic transducer (e.g., the ultrasonictransducer 21) to control the ultrasonic transducer to transmit anultrasonic wave to an object (e.g., subject 200) and detects a receptionvoltage signal generated at a second terminal (the second terminal 21 b)of the ultrasonic transducer by the ultrasonic wave reflected by theobject. The ultrasonic sensor (the ultrasonic probe 1) includes:

a first voltage output unit (for example, the driver 11 or the firstdrive circuit 11A) connected to the first terminal of the ultrasonictransducer and configured to output a transmission voltage signal thatoscillates between a first high voltage (Vdd1, e.g., 40V) and a firstlow voltage (Vss1, e.g., 0V) in accordance with a given transmissionfrequency; and

a reception circuit (e.g., the reception circuit 12) connected to thesecond terminal of the ultrasonic transducer and configured to detect areception voltage signal generated at the second terminal. The firstvoltage output unit includes a first switching unit (e.g., the switchingelements SWA and SWB) configured to perform switching between supplyingthe transmission voltage signal output from the first voltage outputunit to the first terminal in ultrasonic transmission and maintaining apotential of the first terminal in ultrasonic reception. The ultrasonicsensor further includes a second voltage output unit (19) connected tothe second terminal of the ultrasonic transducer and configured tooutput a second high voltage (Vdd2, e.g., 3 V, 1.2 V) having the samepolarity as the power supply voltage (for example, 3 V, 1.2 V) of thereception circuit and having a smaller absolute value than the firsthigh voltage. The second voltage output unit (19) includes a secondswitching unit (e.g., the switching elements SW4, SWC, and SWD)configured to perform switching between supplying the second highvoltage output from the second voltage output unit to the secondterminal in ultrasonic transmission and electrically separating thesecond voltage output unit from the second terminal in ultrasonicreception.

In the comparative ultrasonic sensor described above with reference toFIG. 7 , the second terminal of the ultrasonic transducer is grounded,the driver that applies a transmission signal (first voltage outputunit) is connected to the first terminal of the ultrasonic transducer,and the reception circuit is connected, via the switching element, tothe first terminal of the ultrasonic transducer. The comparativeultrasonic sensor turns off the switching element in ultrasonictransmission, thereby electrically separating the reception circuit fromthe ultrasonic transducer, so as to prevent application, to thereception circuit, of a high voltage of the transmission voltage signalof the driver circuit. In ultrasonic reception, the application of thetransmission voltage signal from the driver circuit is turned off, theswitching element is turned on, and the reception circuit detects thereception voltage signal generated at the second terminal of theultrasonic transducer.

In the ultrasonic sensor, since a high voltage (first high voltage) isapplied to the first terminal of the ultrasonic transducer in ultrasonictransmission, a semiconductor element having a high withstand voltage isused in a driver circuit (first voltage output unit) connected to thefirst terminal. The driver circuit using a semiconductor element havinga high withstand voltage has a large parasitic capacitance. Therefore,in the ultrasonic sensor in which the reception circuit is connected tothe first terminal of the ultrasonic transducer via the switchingelement, the electric charge generated in the ultrasonic transducerflows into the parasitic capacitance in the driver circuit in ultrasonicreception, and the reception voltage signal transmitted to the receptioncircuit is weakened. As a result, the reception sensitivity of theultrasonic sensor is lowered.

In the ultrasonic sensor in which the reception circuit is connected tothe first terminal of the ultrasonic transducer via the switchingelement, a weak reception voltage signal generated in the ultrasonictransducer in ultrasonic reception is transmitted to the receptioncircuit via the switching element. Therefore, undesirably, the S/N ratioof the reception voltage signal transmitted to the reception circuitdecreases due to the noise of the switching element.

On the other hand, in the ultrasonic sensor according to this aspect,the first voltage output unit is connected to the first terminal (21 a)of the ultrasonic transducer, and the reception circuit (12) isconnected to the second terminal (21 b) of the ultrasonic transducer,similar to the comparative ultrasonic sensor illustrated in FIG. 8 .This configuration prevents the reception signal transmitted to thereception circuit from being weakened due to the parasitic capacitanceof the first voltage output unit including a semiconductor elementhaving a high withstand voltage and the first switching unit.Accordingly, degradation of the reception sensitivity of the ultrasonicsensor is prevented.

Further, in the ultrasonic sensor according to this aspect, no switchingelement is present between the second terminal (21 b) of the ultrasonictransducer and the reception circuit (12), similar to the comparativeultrasonic sensor illustrated in FIG. 8 . Therefore, a weak receptionvoltage signal generated in the ultrasonic transducer in ultrasonicreception is transmitted to the reception circuit without passingthrough the switching element. This configuration eliminates a decreasein the S/N ratio of the reception signal caused by the switchingelement.

In the comparative ultrasonic sensor illustrated in FIG. 8 , the secondterminal (21 b) of the ultrasonic transducer is grounded via a switch.In a case where the switch is a semiconductor element, there is a riskthat a voltage out of an allowable voltage range is applied to thereception circuit in ultrasonic transmission.

More specifically, generally, an ultrasonic transducer can be understoodas a capacitance model (to be precise, an LCR model). A currentinstantaneously flows through the ultrasonic transducer when (atcharging) the voltage applied to the first terminal (21 a) of theultrasonic transducer switches from the first low voltage (e.g., 0 V)having a small absolute value to the first high voltage (e.g., 40 V)having a large absolute value and when (at discharging) the voltageswitches from the first high voltage (e.g., 40 V) to the first lowvoltage (0 V). At this time, in a configuration in which the switch is,for example, an n-type metal-oxide semiconductor (MOS) transistor(semiconductor element), the potential of the second terminal of theultrasonic transducer remains within the range of Vss (0 V)+α V evenwhen an instantaneous current flows at the switching (at charging) ofthe voltage applied to the first terminal of the ultrasonic transducerfrom the high voltage (40 V) to the low voltage (0 V). However, at theswitching (at discharge) from the high voltage (40 V) to the low voltage(0 V), an instantaneous current flows. Then, the potential of the secondterminal of the ultrasonic transducer becomes lower than Vss (0 V) andreaches about −0.7 V at which the body diode is turned on. For thisreason, a negative voltage (having a polarity opposite to that of thepower supply voltage of the reception circuit) outside the allowablevoltage range is applied to the reception circuit.

Therefore, in this aspect, the second voltage output unit to output thesecond high voltage is connected to the second terminal of theultrasonic transducer. The second high voltage has the same polarity asthe power supply voltage of the reception circuit and has an absolutevalue smaller than that of the first high voltage (output from the firstvoltage output unit) applied to the first terminal of the ultrasonictransducer. In ultrasonic transmission, the second switching unitsupplies the second high voltage output from the second voltage outputunit to the second terminal of the ultrasonic transducer. In thisconfiguration, at the switching of the voltage applied to the firstterminal of the ultrasonic transducer from the first high voltage to thefirst low voltage (at discharge), even when an instantaneous currentflows, the second terminal of the ultrasonic transducer has a potentiallowered by about α V (α<1 V) from the second high voltage. Setting thesecond high voltage to have an absolute value equal to or greater than αcan prevent application of a negative voltage (having a polarityopposite to that of the power supply voltage of the reception circuit)outside the allowable voltage range to the reception circuit inultrasonic transmission.

However, at the switching of the voltage applied to the first terminalof the ultrasonic transducer from the first low voltage to the firsthigh voltage (at charging), an instantaneous current flows. Then, thepotential of the second terminal of the ultrasonic transducer rises fromthe second high voltage by about 0.7 V. This voltage is applied to thereception circuit. At this time, if the voltage having increased byabout 0.7 V from the second high voltage exceeds the allowable voltagerange of the reception circuit (for example, a voltage 1.4 times thepower supply voltage of the reception circuit), there is a risk that thereception circuit is broken. Therefore, it is preferable that the secondhigh voltage is set to be equal to or higher than α V and within such arange that the voltage increased from the second high voltage by about0.7 V does not exceed the allowable voltage range of the receptioncircuit.

In particular, as the absolute value of the second high voltageincreases, the difference from the first high voltage decreases, and thetransmission voltage signal applied to the ultrasonic transducer becomesweaker. Therefore, it is preferable that the second high voltage is assmall as possible.

Aspect 2

According to Aspect 2, in the ultrasonic sensor according to Aspect 1,the second high voltage is substantially the same as a power supplyvoltage of the reception circuit.

According to this aspect, the configuration of the ultrasonic sensor issimplified as compared with a case where the second high voltage outputby the second voltage output unit is different from the power supplyvoltage of the reception circuit.

Further, in this aspect, as described above, the second voltage outputunit and the second switching unit are connected to the second terminalof the ultrasonic transducer to which the reception circuit isconnected. Therefore, if the parasitic capacitance due to thesemiconductor element of the second voltage output unit or that of thesecond switching unit is large, in ultrasonic reception, the electriccharge generated in the ultrasonic transducer flows into the parasiticcapacitance of the second voltage output unit or the second switchingunit. Then, the reception voltage signal transmitted to the receptioncircuit is weakened, resulting in degradation of the receptionsensitivity of the ultrasonic sensor.

This aspect eliminates such a risk as follows.

In recent years, there has been a demand for higher frequencies ofultrasonic sensors, and accordingly, speeding up of the circuitoperation of a reception circuit has been desired. In a case where anintegrated circuit that operates in a high frequency band is employed asa reception circuit in order to increase the speed of the circuitoperation, a fine semiconductor element is used in the receptioncircuit. Since the breakdown voltage of each node of the finesemiconductor element is low, the power supply voltage of the receptioncircuit is low. Therefore, in this aspect, in a case where the frequencyof the ultrasonic sensor is increased, the second high voltage appliedto the second terminal of the ultrasonic transducer is as small as thepower supply voltage of the reception circuit using the finesemiconductor element. If the second high voltage applied to the secondterminal of the ultrasonic transducer is as small as the power supplyvoltage of the reception circuit, a fine semiconductor element can beused for the second voltage output unit that uses the second highvoltage and the second switching unit. As a result, the parasiticcapacitance of the second voltage output unit and that of the secondswitching unit are reduced, thereby eliminating the risk of degradationof the reception sensitivity of the ultrasonic sensor.

Aspect 3

According to Aspect 3, in the ultrasonic sensor according to Aspect 1 or2, the second voltage output unit also outputs a second low voltagehaving an absolute value smaller than that of the second high voltage.The second switching unit repeatedly performs, in ultrasonictransmission, supply of the second low voltage from the second voltageoutput unit to the second terminal during a period in which the firsthigh voltage is applied to the first terminal, and supply of the secondhigh voltage from the second voltage output unit to the second terminalduring a period in which the first low voltage is applied to the firstterminal.

In this aspect, the second terminal of the ultrasonic transducer issupplied with a voltage signal that is an inverted signal of thetransmission voltage signal (voltage signal that oscillates between thefirst high voltage and the first low voltage) applied to the firstterminal of the ultrasonic transducer. In this case, at the switching ofthe voltage applied to the first terminal of the ultrasonic transducerfrom the first high voltage to the first low voltage (H to L), thevoltage applied to the second terminal of the ultrasonic transducerswitches from the second low voltage to the second high voltage (L toH). As described above, at the switching of the first high voltage tothe first low voltage (H to L), the current instantaneously flowsthrough the ultrasonic transducer, and the potential of the secondterminal of the ultrasonic transducer is lowered by about 0.7 V. At thistime, in this aspect, since the voltage applied to the second terminalof the ultrasonic transducer is switched from the second low voltage tothe second high voltage (L to H), the second terminal of the ultrasonictransducer is prevented from having a negative potential, andapplication of a negative voltage (voltage having a polarity opposite tothat of the power supply voltage of the reception circuit) to thereception circuit is prevented.

Further, in this aspect, at the switching of the voltage applied to thefirst terminal of the ultrasonic transducer from the first low voltageto the first high voltage (L to H), the voltage applied to the secondterminal of the ultrasonic transducer switches from the second highvoltage to the second low voltage (H to L). At this time, a currentinstantaneously flows through the ultrasonic transducer also at theswitching (L to H) from the first low voltage to the first high voltage,and the potential of the second terminal of the ultrasonic transducer israised by about 0.7 V. At this time, in the present aspect, since thevoltage applied to the second terminal of the ultrasonic transducer isswitched from the second high voltage to the second low voltage (H toL), the potential of the second terminal of the ultrasonic transducerlowers from the second high voltage. Therefore, the potential of thesecond terminal of the ultrasonic transducer is prevented from risingfrom the second high voltage by about 0.7 V, and is kept at a potentialequal to or lower than the second high voltage. Therefore, even when thereception circuit employs a fine semiconductor element and has a lowpower supply voltage, application of an overvoltage exceeding theallowable voltage range to the reception circuit is prevented.

Aspect 4

According to Aspect 4, in the ultrasonic sensor according to Aspect 3,in ultrasonic transmission, the second switching unit starts supplyingthe second low voltage output from the second voltage output unit to thesecond terminal before the start of application of the first highvoltage to the first terminal, and starts supplying the second highvoltage output from the second voltage output unit to the secondterminal before the start of application of the first low voltage to thefirst terminal.

At transmission, when the voltage applied to the first terminal of theultrasonic transducer is switched from the first high voltage to thefirst low voltage (H to L), a current instantaneously flows through theultrasonic transducer, and the potential of the second terminal of theultrasonic transducer is lowered by about 0.7 V. At this time, thevoltage applied to the second terminal of the ultrasonic transducer isswitched from the second low voltage to the second high voltage (L toH). If this switching is delayed, the second terminal of the ultrasonictransducer has a negative potential, and there is a risk that a negativevoltage (voltage having a polarity opposite to that of the power supplyvoltage of the reception circuit) is applied to the reception circuit.

In this aspect, in ultrasonic transmission, the supply of the secondhigh voltage output from the second voltage output unit to the secondterminal starts earlier than the start of application of the first lowvoltage to the first terminal (H to L). This configuration reliablyprevents delay of switching from the second low voltage to the secondhigh voltage from the switching (H to L) of the voltage applied to thefirst terminal. This configuration reliably prevents application of anegative voltage (voltage having a polarity opposite to that of thepower supply voltage of the reception circuit) to the reception circuit.

Similarly, in ultrasonic transmission, when the voltage applied to thefirst terminal of the ultrasonic transducer is switched from the firstlow voltage to the first high voltage (L to H), a currentinstantaneously flows through the ultrasonic transducer, and thepotential of the second terminal of the ultrasonic transducer is raisedby about 0.7 V. At this time, the voltage applied to the second terminalof the ultrasonic transducer is switched from the second high voltage tothe second low voltage (H to L). If this switching is delayed, thepotential of the second terminal of the ultrasonic transducer is raisedby about 0.7 V from the second high voltage, and there arises a riskthat an overvoltage exceeding the allowable voltage range is applied tothe reception circuit employing a fine semiconductor element and havinga low power supply voltage.

In this aspect, in ultrasonic transmission, the supply of the second lowvoltage output from the second voltage output unit to the secondterminal starts earlier than the start of application of the first highvoltage to the first terminal (switching from L to H). Such controlreliably prevents delay of the switching from the second high voltage tothe second low voltage from the switching from the first low voltage tothe first high voltage (L to H). Such control more reliably preventsapplication of an overvoltage exceeding the allowable voltage range tothe reception circuit.

Aspect 5

According to Aspect 5, in the ultrasonic sensor of any one of Aspects 1to 4, the second switching unit includes: a first MOS transistor (forexample, the switching element SWC) in which one of the drain and sourceterminals is supplied with the second high voltage (Vdd2); and a secondMOS transistor (for example, the switching element SWD) in which one ofthe drain and source terminals is supplied with a ground voltage, andthe other of the drain and source terminals of the first MOS transistorand the other of the drain and source terminals of the second MOStransistor are connected to the second terminal of the ultrasonictransducer. In ultrasonic transmission, the second switching unitsupplies, to the gate terminals pg2 and ng2, gate voltages for turningon the first MOS transistor and the second MOS transistor, respectively.In ultrasonic reception, the second switching unit supplies, to the gateterminals, gate voltages for turning off the first MOS transistor andthe second MOS transistor, respectively.

This configuration enables use of a fine semiconductor element for thesecond switching unit and reduces the parasitic capacitance of thesecond switching unit. Accordingly, degradation of the receptionsensitivity of the ultrasonic sensor is eliminated.

Aspect 6

According to Aspect 6, in the ultrasonic sensor of Aspect 5, the firstvoltage output unit includes: a third MOS transistor (for example, theswitching element SWA) in which one of the drain and source terminals issupplied with the first high voltage; and a fourth MOS transistor (forexample, the switching element SWB) in which one of the drain and sourceterminals is supplied with the first low voltage, and the other of thedrain and source terminals of the third MOS transistor and the other ofthe drain and source terminals of the fourth MOS transistor areconnected to the first terminal of the ultrasonic transducer. The firstvoltage output unit repeats turning on and off of the third MOStransistor and turning off and on of the fourth MOS transistor accordingto a predetermined transmission frequency, thereby outputting thetransmission voltage signal.

According to this aspect, the first voltage output unit is implementedby the MOS transistors.

Aspect 7

According to Aspect 7, in the ultrasonic sensor of Aspect 6, the firstswitching unit includes the third MOS transistor and the fourth MOStransistor, repeats turning on and off of the third MOS transistor andturning off and on of the fourth MOS transistor according to apredetermined transmission frequency in ultrasonic transmission, andkeeps one of the third MOS transistor and the fourth MOS transistor onin ultrasonic reception, thereby maintaining the potential of the firstterminal.

According to this aspect, since the third MOS transistor and the fourthMOS transistor of the first voltage output unit serves as the firstswitching unit, the configuration is simplified and reduced in size ascompared with a case where the first switching unit is a separatecomponent from the first voltage output unit.

Aspect 8

According to Aspect 8, in the ultrasonic sensor of Aspect 6 or 7, thereception circuit includes a MOS transistor, each of the first MOStransistor and the second MOS transistor includes a gate insulating filmhaving a thickness thinner than a thickness of a gate insulating film ofeach of the third MOS transistor and the fourth MOS transistor and isthe same as a thickness of a gate insulating film of the MOS transistorof the reception circuit.

According to this aspect, since a fine semiconductor element can be usedfor the second switching unit and the parasitic capacitance of thesecond switching unit can be reduced, deterioration of the receptionsensitivity of the ultrasonic sensor is prevented.

Aspect 9

According to Aspect 9, in the ultrasonic sensor of any one of Aspects 6to 8, the first MOS transistor and the second MOS transistor have a gatechannel length shorter than a gate channel length of the third MOStransistor and the fourth MOS transistor.

According to this aspect, since a fine semiconductor element can be usedfor the second switching unit and the parasitic capacitance of thesecond switching unit can be reduced, deterioration of the receptionsensitivity of the ultrasonic sensor is prevented.

Aspect 10

According to Aspect 10, in the ultrasonic sensor of any one of Aspects 1to 10, the ultrasonic transducer is a piezoelectric micro-machinedultrasonic transducer (PMUT) or a capacitive micro-machined ultrasonictransducer (CMUT).

According to this aspect, an ultrasonic sensor having a largetransmission intensity is realized.

Aspect 11

Aspect 11 concerns an ultrasonic image generating apparatus thatincludes the ultrasonic sensor according to any one of Aspects 1 to 10,and an image generation unit (for example, the image processor 65) thatgenerates an image based on the reception voltage signal received by thereception circuit of the ultrasonic sensor.

According to this aspect, application of a voltage out of the allowablevoltage range to the reception circuit in ultrasonic transmission isprevented, and an appropriate ultrasonic image is generated.

Aspect 12

Aspect 12 concerns an ultrasonic diagnostic apparatus that includes theultrasonic sensor according to any one of Aspects 1 to 10, and a display(e.g., the display 61) that displays a shape of the object.

According to this aspect, application of a voltage out of the allowablevoltage range to the reception circuit at transmission of ultrasonicwaves is inhibited, and the shape of the target object is appropriatelydisplayed.

The above-described embodiments are illustrative and do not limit thepresent invention. Thus, numerous additional modifications andvariations are possible in light of the above teachings. For example,elements and/or features of different illustrative embodiments may becombined with each other and/or substituted for each other within thescope of the present invention.

1. An ultrasonic sensor comprising: an ultrasonic transducer; a firstvoltage output circuit connected to a first terminal of the ultrasonictransducer and configured to output a transmission voltage signal thatoscillates between a first high voltage and a first low voltage lowerthan the first high voltage, in accordance with a transmissionfrequency, the transmission voltage signal to be supplied to the firstterminal of the ultrasonic transducer to control transmission of anultrasonic wave from the ultrasonic transducer to an object, the firstvoltage output circuit including a first switching unit configured toperform switching between: supplying the transmission voltage signaloutput from the first voltage output circuit to the first terminal inultrasonic transmission; and fixing a potential of the first terminal inultrasonic reception; a reception circuit connected to a second terminalof the ultrasonic transducer and configured to detect a receptionvoltage signal generated at the second terminal by the ultrasonic wavereflected by the object; and a second voltage output circuit connectedto the second terminal of the ultrasonic transducer and configured tooutput a second high voltage having a same polarity as a power supplyvoltage of the reception circuit, the second high voltage having anabsolute value smaller than an absolute value of the first high voltage,the second voltage output circuit including a second switching unitconfigured to perform switching between: supplying the second highvoltage to the second terminal in ultrasonic transmission; andelectrically separating the second voltage output circuit from thesecond terminal in ultrasonic reception.
 2. The ultrasonic sensoraccording to claim 1, wherein the second high voltage is equal to thepower supply voltage of the reception circuit.
 3. The ultrasonic sensoraccording to claim 1, wherein the second voltage output circuit furtheroutputs a second low voltage having an absolute value smaller than theabsolute value of the second high voltage, and wherein, in ultrasonictransmission, the second switching unit repeatedly performs supplyingthe second low voltage to the second terminal during a period in whichthe first high voltage is supplied to the first terminal and supplyingthe second high voltage to the second terminal during a period in whichthe first low voltage is supplied to the first terminal.
 4. Theultrasonic sensor according to claim 3, wherein, in ultrasonictransmission, the second switching unit: starts supplying the second lowvoltage output to the second terminal prior to start of supplying thefirst high voltage to the first terminal; and starts supplying thesecond high voltage output to the second terminal prior to start ofsupplying the first low voltage to the first terminal.
 5. The ultrasonicsensor according to claim 1, wherein the second switching unit includes:a first metal oxide semiconductor (MOS) transistor in which one of adrain terminal and a source terminal is supplied with the second highvoltage; and a second MOS transistor in which one of a drain terminaland a source terminal is supplied with a second low voltage having anabsolute value smaller than the absolute value of the second highvoltage, wherein the other of the drain terminal and the source terminalof the first MOS transistor and the other of the drain terminal and thesource terminal of the second MOS transistor are connected to the secondterminal of the ultrasonic transducer, wherein, in ultrasonictransmission, the second switching unit supplies, to gate terminals ofthe first MOS transistor and the second MOS transistor, gate voltagesfor turning on the first MOS transistor and the second MOS transistor,and, wherein, in ultrasonic reception, the second switching unitsupplies, to the gate terminals of the first MOS transistor and thesecond MOS transistor, gate voltages for turning off the first MOStransistor and the second MOS transistor.
 6. The ultrasonic sensoraccording to claim 5, wherein the first voltage output circuit includes:a third MOS transistor in which one of a drain terminal and a sourceterminal is supplied with the first high voltage; and a fourth MOStransistor in which one of a drain terminal and a source terminal issupplied with the first low voltage, wherein the other of the drainterminal and the source terminal of the third MOS transistor and theother of the drain terminal and the source terminal of the fourth MOStransistor are connected to the first terminal of the ultrasonictransducer, and wherein the first voltage output circuit repeats turningon and off of the third MOS transistor and turning off and on of thefourth MOS transistor in accordance with the transmission frequency, soas to output the transmission voltage signal.
 7. The ultrasonic sensoraccording to claim 6, wherein the first switching unit includes thethird MOS transistor and the fourth MOS transistor, and wherein, inultrasonic reception, one of the third MOS transistor and the fourth MOStransistor is kept on so as to fix the potential of the first terminal.8. The ultrasonic sensor according to claim 6, wherein the receptioncircuit includes a MOS transistor, and wherein each of the first MOStransistor and the second MOS transistor includes a gate insulating filmhaving a thickness thinner than a thickness of a gate insulating film ofeach of the third MOS transistor and the fourth MOS transistor and issame as a thickness of a gate insulating film of the MOS transistor ofthe reception circuit.
 9. The ultrasonic sensor according to claim 6,wherein each of the first MOS transistor and the second MOS transistorhas a gate channel length shorter than a gate channel length of each ofthe third MOS transistor and the fourth MOS transistor.
 10. Theultrasonic sensor according to claim 1, wherein the ultrasonictransducer is a piezoelectric micro-machined ultrasonic transducer or acapacitive micro-machined ultrasonic transducer.
 11. An ultrasonic imagegenerating apparatus comprising: the ultrasonic sensor according toclaim 1; and an image processing circuit configured to generate an imagebased on the reception voltage signal received by the reception circuitof the ultrasonic sensor.
 12. An ultrasonic diagnostic apparatuscomprising: the ultrasonic sensor according to claim 1; an imageprocessing circuit configured to generate an image based on thereception voltage signal received by the reception circuit of theultrasonic sensor; and a display configured to display the imagegenerated by the image processing circuit, the image representing ashape of the object.